1. Field of the Invention
The gage diameter of the rock bit determines the size of the bit and the hole which it drills and is of primary importance in the drilling art.
The gage tolerance standard set by the American Petroleum Institute (API) is the nominal gage to plus 0.031 inch for bit sizes ranging from 33/8 to 133/4 inches and nominal gage to plus 0.062 inch for bit sizes from 14 to 171/2 inches in diameter.
During drilling operations on a drill rig, the drill string is often removed from the hole to change the drill bit type or replace a dull bit. Drill bit cutters, or cones, are designed to maintain the gage diameter even as wear occurs. If the hole diameter is undergage, the following replacement bit will have to ream its way to the hole bottom before starting to drill a new hole. Conversely, the gage of the replacement bit must be within the foregoing tolerance otherwise the new bit, if it is oversize, might not pass down the hole without jamming or causing damage to the well bore. Therefore, the rock bit must be manufactured to exacting standards.
Accordingly, this invention relates to the fabrication process of rock bits with a plurality of rolling cutters wherein the gage diameters must be held within close tolerances.
More specifically, this invention relates to an electronic means to monitor the gage and height of rock bits during the welding process wherein two and three segment rock bits containing individual cones are joined together by metallurgical bonding.
2. Description of Prior Art
Prior art methods to determine the gage of rock bits traditionally utilized go or no-go rings that are slipped over the gage of the rock bit, the bit comprising up to three segments which contain the cones mounted on journals of each of the legs.
For example, U.S. Pat. No. 3,907,191 describes a ring gage which is positioned around the individual leg segments, the individual segments are moved relative to one another causing the parting face of an individual segment to slide against the parting face of an adjacent segment. The segments are moved until the gage cutting surfaces of the segments physically contact a ring gage, thereby insuring that the finished bit will have the desired gage size. These segments are then subsequently welded together over a substantial portion of the parting faces.
This invention is disadvantaged in that the preset mechanical assembly is not monitored during the welding cycle hence the segments could move and any misalignment would not be discovered until the welded assembly is subsequently inspected. A rock bit which is out of gage must be disassembled and rewelded which, of course, is a costly and time consuming process.
The instant invention overcomes this difficulty in that the welding process may be continually monitored by, for example, a non-contacting light beam and light sensitive sensor element. The welding process may then be immediately stopped when an out of gage condition is detected. Adjustments can be made before the weld has gone beyond a point in which the rock bit must be disassembled and rewelded.
An advantage is realized over the prior art in the use of a continuous non-contact measurement system wherein both the gage dimension, bit concentricity and bit height is electronically monitored during the weld process. Radial translation of the bit leg segments to gage is possible using the foregoing systems. True bit geometry is assured by proper journal alignment in the bit carriers when the bit leg segments are initially assembled in a welding fixture.